1. Field of the Invention
The invention disclosed in this specification relates to a control apparatus and a control method for an internal combustion engine.
2. Description of Related Art
In a secondary air supply device available in the related art, air is delivered to an exhaust port of an internal combustion engine from the outside, exhaust gas in and beyond the exhaust port is oxidized by causing oxygen (O2) in the air to react with the exhaust gas, and as a result, an amount of discharged unburned gas such as hydrocarbon (HC) and carbon monoxide (CO) is reduced. When, in this type of secondary air supply device, a malfunction occurs in an air pump (A/P) or an air switching valve (ASV), a blockage occurs in a flow passage for supplying secondary air, and so on, the air is not delivered normally to the exhaust port, and as a result, exhaust gas emissions from the internal combustion engine increase. Hence, an abnormality diagnosis (On-Board Diagnostics (OBD)) is performed on the secondary air supply device. Japanese Patent Application Publication No. 2003-83048 (JP-2003-83048 A) discloses an abnormality diagnosis for a secondary air supply device, in which, for example, pressure behavior patterns determined from a pressure value and a pressure variation value detected by a pressure sensor disposed between the A/P and the ASV are determined respectively when secondary air supply is underway and when secondary air supply is stopped. A condition of the secondary air supply device is then determined on the basis of variation in the pressure behavior patterns in the respective cases. Here, when foreign matter becomes caught in the ASV, it may be determined that that the ASV is stuck in an open condition, and as a result, an abnormality may be diagnosed.
Incidentally, secondary air supply (Air Injection (AI)) to be referred to as AI hereafter) control is typically performed during a cold start of the internal combustion engine. When the internal combustion engine performs a cold start, ice formed in a pipe for supplying the secondary air may move toward the ASV, and as a result, the ice as foreign matter may become caught between a housing and a valve body of the ASV. When an abnormality diagnosis is performed in a condition where ice is caught in the ASV, it is determined that an open sticking abnormality has occurred in the ASV. When the foreign matter is ice, however, the ice melts as a peripheral temperature increases, making it difficult to find out the cause of the abnormality during an inspection of the ASV. In a case where an abnormality is detected but the cause thereof cannot be specified, component replacement is required.
A similar problem may occur with foreign matter other than ice. More specifically, it may be determined that an open sticking abnormality has occurred even though the caught foreign matter has been removed, thereby eliminating the abnormality such that in actuality, an abnormality has not occurred in the ASV. Likewise in this case, it is difficult to find out the cause of the abnormality during an inspection of the ASV, and since the cause remains unidentified, component replacement is required.